Downlights are light fixtures that are installed in a hollow opening within a ceiling to provide inconspicuous light that appears to shine from a hole in the ceiling. The downlight generally includes a housing mounted in the ceiling and a lighting module removably attachable to the housing. The lighting module generally includes a light source, such as one or more LEDs, compact fluorescent lamps (“CFLs”), high-intensity discharge (“HID”) lamps, or incandescent lamps.
Downlights sometimes employ small, very bright light sources. These tiny, bright light sources should be diffused to the viewer while being efficient and not sacrificing a large portion of the light output. Flat glass lenses have been used in downlights in the past to diffuse the light sources, particularly with HID light sources. These flat glass lenses typically utilize prismatic elements on either side of the lens that diffuse the light source. However, the light diffusion provided by flat lenses fails to provide adequate uniform luminance as the light transmitted by flat lenses is generally significantly more intense near the center of the lens than at outer points of the lens.